This invention relates to fire protection materials, such as coatings for steel or other structural members, and to methods of making these materials.
Steel beams and other structural members in buildings are commonly coated with a fire protective material to enhance their fire resistance. Currently commercially available materials used to provide these insulating coatings are generally cementitious, and are typically applied (e.g. to a steel beam surface) in a layer about one inch thick. A conventional coating of this type on a steel surface will ordinarily be effective to keep the temperature of the steel substrate below 1000.degree. F. for at least about one hour of continuous exposure of the coating surface to a temperature of 2000.degree. F. It will be understood that the coating of steel structural members represents an especially important field of use of fire protection materials as contemplated herein, but such materials may also be employed to coat surfaces of wood or other substances and in some instances even to constitute fire protection layers or bodies other than coatings.
While present-day materials are capable of affording substantial fire protection, their use has been attended with various problems. For instance, when applied they require a relatively long time to set, and cannot be applied or used satisfactorily at low temperatures, e.g. in cold-weather conditions in unheated buildings. The attainment of a satisfactory coating bond to a substrate (e.g. steel) surface has frequently been troublesome. Moreover, coatings of these known compositions require special protection against accidental impacts and other hazards of normal construction as they are quite fragile and their integrity is easily destroyed. In addition, they tend not to endure exposure to fire well enough to be able to be patched and used thereafter for continued fire protection service.
It has heretofore been known that fast-setting structures having advantageous properties for diverse uses can be produced by mixing, with a magnesia-containing aggregate, ammonium phosphates in aqueous solution, provided that the composition of the phosphates includes a substantial proportion of polyphosphates. In these structures there is chemical bonding involving the magnesia and the phosphates. U.S. Pat. No. 3,879,209 and No. 4,059,455 describe methods of producing concrete structures by establishing such a mixture and allowing it to set for an extended period at ambient atmospheric temperature. The structures thus produced progressively develop hydraulic strength, form strong bonds with existing concrete or other surfaces, and have low porosity so as to be capable of outdoor load-bearing use e.g. for paving or repairing roadways. U.S. Pat. No. 3,285,758 and No. 3,413,385 describe methods of making or repairing refractory furnace linings or walls with such mixtures, wherein the produced structure is exposed to elevated temperature during or shortly after application of the mixture.
The magnesia-polyphosphate chemical bonding systems of the mixtures described in the aforementioned patents provide very rapid setting even at low ambient temperatures (cold weather conditions), good adherence to metal and other surfaces, and sufficient strength in the produced structures to withstand substantial impacts without loss of integrity. The bulk density of the specifically described concrete and furnace lining structures, however, is far too high (on the order of 150 lb./ft..sup.3 or above), and their thermal conductivity is correspondingly too great, for use of these mixtures as fire protection materials for structural members and the like; i.e. whereas fire protection coatings for steel beams are necessarily relatively thin, owing to considerations of space and weight, such thin coatings of the mixtures specifically described in the aforementioned patents would not afford adequate insulating effect to satisfy fire protection requirements.